1. Field of the Invention
The present invention relates to a plasma antenna for a plasma processing apparatus, and, more particularly, to a plasma antenna, designed to allow connection between electric elements of the antenna to be varied without changing the construction of the antenna during a chemical vapor deposition process, thereby maximizing efficiency of a cleaning or deposition process.
2. Description of the Prior Art
In manufacture of semiconductor devices, various plasma deposition and etching have been developed. This is attributed to the fact that, in comparison to a commonly used chemical vapor deposition process, the plasma deposition process can be performed at a lower deposition temperature and a higher deposition speed due to activation of reactant gases by the plasma. Additionally, the plasma deposition or etching process can be performed more easily by appropriately applying a relative bias to a plasma electrode or a susceptor.
As for a plasma processing apparatus, an inductive coupled plasma processing apparatus, and a capacitive coupled plasma processing apparatus have been widely employed. Additionally, a new type of plasma processing apparatus, which has an electric field generator coupled to basic components of the typical plasma processing apparatus, has been developed.
The conventional inductive coupled plasma processing apparatus employs a single helical antenna or a plurality of separated coil antennas. As RF power is applied to the antenna, a time-variable magnetic field is generated perpendicular to a plane constituted by the antenna, and induces an electric field within a chamber. Then, the electric field heats electrons to generate plasma. That is, as the electrons collide with surrounding neutral gaseous particles, ions and radicals are generated, which are used for plasma etching or deposition. Furthermore, it is possible to control the energy of ion beams incident to a specimen through application of power to a wafer chuck by use of a separate high frequency power source.
FIG. 1 is a schematic view illustrating the overall construction of a semiconductor processing apparatus using an inductive coupled plasma antenna 17 as an example of the conventional plasma processing apparatus.
Referring to FIG. 1, the plasma antenna 17 is equipped on a vacuum chamber 11 for generating plasma in order to perform a deposition process or to remove a coated film on the surface of an object within the chamber during the process. The plasma antenna 17 is equipped with an insulating plate (not shown), which is highly conducive so as to transfer the energy from an RF power source to the plasma through inductive coupling by reducing capacitive coupling between the antenna and the plasma. Meanwhile, the plasma antenna 17 is connected to an impedance matching device 35, which is connected to an RF power source 37. Furthermore, the chamber 11 is formed with a gas injection port 27 for supplying a cleaning gas or a deposition gas, and is equipped at a lower portion with a wafer chuck 29 upon which a wafer to be subjected to deposition is located. Additionally, the vacuum chamber 11 is further formed with an exhaust port (not shown) through which the gas is exhausted to the outside. With such a construction of the inductive coupled plasma processing apparatus 10, initially, the vacuum chamber 11 is evacuated to below a predetermined vacuum level by use of a vacuum pump (not shown), and supplied with a reactant gas for generating the plasma through the gas injection port 27 such that a predetermined pressure is maintained. Then, RF power is applied to the plasma antenna 17 from the RF power source 37. As such, with the plasma processing apparatus, the plasma can be generated by applying an appropriate RF power in a single frequency band or in various frequency bands to an antenna for generating the inductive coupled plasma, such as the plasma antenna 17, surrounding the vacuum chamber.
Meanwhile, the plasma processing apparatus for a cleaning or depositing process used for semiconductor manufacturing equipment employs a helical antenna, as shown in FIGS. 2a and 3a in which a single or a plurality of coils constituting the antenna are connected in series and in parallel, respectively.
In FIG. 2a, an RF power source 41 is connected to a helical antenna of a series circuit through an impedance matching circuit 40. In this construction, since respective coils of the antenna are connected in series, a constant electrical current flows through the respective coils. However, since the constant electrical current flows through the respective coils, it is difficult to control distribution of an inductive electric field. Additionally, since the respective coils constituting the antenna are connected in series, causing voltage drop to be increased by the antenna, an influence attributed to capacitive coupling with the plasma is increased.
Thus, loss of ions and electrons occurs adjacent to an inner wall of the chamber, whereby the plasma is increased in density at the center thereof while being decreased in density at portions adjacent to the inner wall of the chamber.
FIG. 2b is an equivalent circuit diagram of FIG. 2a, in which the RF power source 41 is applied to impedances Z1, Z2, Z3 and Z4 of the respective coils. Here, in the case where the antenna constitutes a series circuit, since the respective coils are connected in series, the sum of the impedances of the respective coils is larger than that of the antenna constituting a parallel circuit in which the respective coils are connected in parallel. As a result, the insulating plate equipped between the antenna and the vacuum chamber can be damaged due to the plasma.
In FIGS. 3a and 3b, a variable capacitor for resonance is connected to a point g of the outermost coil of the antenna 52 having helical windings connected in parallel, and acts to control electric current in the antenna 52, thereby providing plasma having a uniform density. Accordingly, even if the frequency of the power for the plasma supplied to the antenna is increased, the problem of impedance matching does not occur. In this case, when the antenna is employed under a higher vacuum level of several mTorr, it generates plasma exhibiting desirable characteristics, whereas when the antenna is employed under a lower vacuum level of several Torr, it often generates partially concentrated plasma, thereby partially damaging the object to be processed. The primary cause of this is a constructional problem causing the RF power to be concentrated on a specific coil.
As for another construction of the antenna, there is an antenna having a plurality of side coils together with a plurality of coils connected in series, in which independent power sources are applied to the respective coils, and require matching boxes for impedance matching, respectively, thereby complicating the construction of the antenna.